1. Field of the Invention
The present invention relates to a technique for dividing and transmitting moving image data via a wired or wireless network.
2. Description of the Related Art
In recent years, network users commonly view moving images via a communication line such as the Internet along with development in a communication system.
In general, a communication protocol called “real-time transport protocol (RTP)” is used for transferring moving image data, in particular, the moving image data that requires real-time communication, such as a live image. The RTP is a protocol for transferring sounds, moving images, or other data in real time. The RTP protocol is defined as request for comments (RFC) 1889 and RFC 1890 by the Internet Engineering Task Force (IETF).
The RTP protocol does not always ensure high data reliability but a low layer protocol such as a user datagram protocol/internet protocol (UDP/IP) which can achieve a relatively-high communication speed is used. In a case of using the UDP/IP or other such protocols, these protocols excel in the real-time communication and efficiency when using a communication band but tend to cause an error such as a packet by its nature.
As a solution to this problem, a technique for suppressing occurrences of the error has been discussed. For example, a data loss appears due to a buffer overflow in a router on a network path and a technique for reducing the data loss by averaging packet transmission intervals has been discussed. In addition, a highly-reliable communication line has been proposed from a viewpoint of communication.
However, even if these techniques are applied, when network congestion or the like actually occurs, it is difficult to reduce a rate of occurrence of the packet loss to zero. Japanese Patent Application Laid-Open No. 11-331839 discusses a technique for determining a level of importance of moving image data on a frame basis using intraframe positional information, and transmitting the data in a descending order of the importance to reduce a packet loss in a highly-important portion.
However, the above conventional technique that determines the importance level of the data in each frame is not necessarily appropriate depending on methods for encoding moving image data or methods for controlling transmission timing of packets.
To be specific, data transmission on a network tends to lose a packet at particular transmission timing or in a particular transmission position depending on a processing sequence for packet transmission timing control. Therefore, in transmission of moving image data, when importance level of the data is determined based on intraframe positional information and the data is transmitted in a descending order of the importance level, two or more pieces of data in a same position in one frame cannot be correctly and continuously reproduced. As a result, an error portion is observable.